All substances have properties that we can use to identify
them. For example we can idenify a person by their face, their
voice, height, finger prints, DNA etc.. The more of these properties
that we can identify, the better we know the person. In a similar
way matter has properties - and there are many of them. There
are two basic types of properties that we can associate with
matter. These properties are called Physical properties
and Chemical properties:

Physical properties:

Properties that do not change
the chemical nature of matter

Chemical properties:

Properties that do change tha
chemical nature of matter

Examples of physical properties are: color, smell,
freezing point, boiling point, melting point, infra-red spectrum,
attraction (paramagnetic) or repulsion (diamagnetic) to magnets,
opacity, viscosity and density. There are many more examples.
Note that measuring each of these properties will not alter the
basic nature of the substance.

The more properties we can identify for a substance, the better
we know the nature of that substance. These properties can then
help us model the substance and thus understand how this substance
will behave under various conditions.